The ‘nocebo’ effect: how informed consent can cause unnecessary harm in trials

The requirement of informed consent means that it is an ethical requirement to warn patients about risks of taking part in clinical trials. But recent research shows that the way in which patients are told about these risks can actually cause harm.

Dr Jeremy Howick, Director of the Oxford Empathy Programme, Faculty of Philosophy, and study author, says: ‘Sometimes when we warn patients about negative side effects in a scary way it actually causes the negative side effect - a "nocebo effect".’

A mega-study cited in the paper found that half of the 250,000 patients who took placebo pills (like sugar pills) in clinical trials reported some negative side effects (like pain or nausea but also more serious things). Current requirements for taking informed consent force ethics committees to focus on talking a lot about trial harms. This is understandable from a medico-legal perspective.

Researchers are concerned about ‘outlier’ cases where a patient might say that they were not sufficiently well informed about a potential harm which they experienced. But talking about harms in the wrong way can cause its own harm. This study shows that ethics committees need to take these ‘nocebo’ harms seriously.

There are emerging ways to share risks with patients without causing unnecessary nocebo effects. Foremost among these is positive framing.

Dr Howick says: ‘You can tell a patient, “10% of the people who take this drug have a negative side-effect”, or you can say, “90% of the people don’t have any negative side-effects”. In both cases the information is the same, but the first way leads to more reported side-effects.

‘Ethics committees need to take the reality of nocebo effects into account, and balance the need to inform patients with the need to inform them the right way.’

Read the full paper in the Journal of Medical Ethics: 'Unethical informed consent caused by overlooking poorly measured nocebo effects.'